jonpo

OK so I have a 06 Mustang GT, 5 speed (3.55 final drive) and 18" premium wheels from the factory. Everything's stock. Anyway, I'm driving by one of those signs that shows your speed, and I decided to test it out to see if my speedometer's accurate. So, I set my cruise on 40, but the sign says I'm only going 37. I then reset my average speed on my trip computer and it registers 37 too. I'm glad it registers fast instead of slow(for cops and stuff), but it still bothers me. Anyone else noticed this or am I just crazy?

ohsixgt1217

Quite possible its not just you. Lol id be happy considering it reads fast lol. But maybe your computee wasnt set for the 18's you have? idk possibly tho. Nothing a tune cant adjust. Personally i wouldnt worry about it, unless you are getting a tuner then id adress it

hawgman

Well, your speedo is electronic. Your trip computer ( including average speed reading ) is electronic. They both read from the PCM. So it is going to be a little difficult to compare the reading from the average speed setting in the trip computer to what the needle indicates on the speedometer since they both are controlled by the same source. As for the side of the road radar sign, it could possibly be off my a MPH or two also simply because since it is not used by law enforcement to hand out tickets it doesn't have to be calibrated at regular intervals.

If you truly think it is off by 3 MPH, take it to Ford and have them check it. Or you could also take it to a dyno shop and do a pull and compare the MPH on the dyno to what your speedo says. The dyno is going to give you an accurate speed reading.

howarmat

+1 to the dyno idea but I am guessing that it is not actually off because those signs are not accurate.

jonpo

Well I did notice that when I'm at a dead stop, my speedo registers 2-3 mph. So maybe the dial is just a little bit off. If that's so, can it be fixed?